Bacteria – the benign, the bad and the beautiful. Facts : • Bacteria are present almost everywhere from deep in the earth's crust to the polar ice caps and oceans to inside the bodies of plants and animals. • There are more bacteria in your mouth than there are people in the world. • Babies are born with no bacteria in their bodies. • Electronics, cellphones, laptops, keyboards etc. hold a lot of bacteria. Single smartphone screens hold 18 times more bacteria than a toilet handle. • Smell of rain is caused by a bacteria called actinomycetes. • Sweat itself is odourless. It’s the bacteria on the skin that mingles with it and produces body odour. • Horseshoe crab blood is worth US $15000/ L due to its ability to detect bacteria. • Gonorrhea bacteria is the strongest creatures on the earth as they can pull 100,000 times their own weight. Introduction . Bacteria were discovered by Leeuwenhoek in 1676. . They are the primitive forms of life. . They are monerans and comprises a group of prokaryotic organisms which is characterized by: o Peptidoglycan wall o Compacted but naked DNA with attached mesosome o Reserve food material made up of glycogen and fats o Gas vacuoles may occur o All membranes bond cell organelles completely absent o 70S Ribosome occurs . They have varied forms of nutrition. Bacterial cell structure § Cell morphology Structure of a typical bacterial cell Cell Envelope

Outer covering of protoplast of bacterial cell. The cell envelope of bacteria consist 3 components: • Glycocalyx • cell wall • plasma membrane Glycocalyx  Some bacteria have an  Glycocalyx gives sticky additional layer outside character to the cell. of the cell wall called  It is not absolutely essential the Glycocalyx. for survival of bacteria.  This outermost However it has several mucilaginous layer secondary functions: consist of non cellulosic • Prevention of polysaccharides with or desiccation without proteins. • Protection from  It occurs as phagocytes • Slime layer when • Protection from toxic glycocalyx occur in chemicals and drugs the form of loose • Protection from viruses mucilage sheath • Attachment • Capsule when thick • Immunogenicity and tough mucilage • Virulence covering. Cell wall  The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan which is located immediately outside of the cytoplasmic membrane.  Peptidoglycan is made up of a polysaccharide backbone consisting of alternating N- Acetylmuramic acid (NAM) and N- acetylglucosamine (NAG) residues in equal amounts.  Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell Fig: The structure of peptidoglycan. shape.  It is relatively porous and is not considered to be a permeability barrier for small substrates. Types of bacterial cell wall  There are two main types of bacterial cell walls, those of gram-positive bacteria and those of gram-negative bacteria, which are differentiated by their Gram staining characteristics.  Gram-positive cell walls are thick and Gram-negative cell walls are thin peptidoglycan layer adjacent to the cytoplasmic membrane.  Peptidoglycan layer constitutes almost 95% of the cell wall in some gram-positive bacteria and as little as 5-10% of the cell wall

in gram-negative bacteria. Fig: Structure of bacterial cell wall Cell membrane  The plasma membrane or bacterial cytoplasmic membrane is composed of a phospholipid bilayer and thus has all of the general functions of a cell membrane.  It is selectively permeable.  It is metabolically active as it takes part in respiration, synthesis of lipids and cell wall Fig: Bacterial cell membrane components. Mesosome

 Multi-laminated structure formed invaginations of plasma membrane.  Principal sites of respiratory enzymes.  Coordinate nuclear & cytoplasmic division during binary fission.  More prominent in Gram +ve bacteria. Fig : structure of mesosome Ribosome

 Bacteria and archaebacteria have smaller ribosomes, termed 70S ribosomes, which are composed of a small 30S subunit and large 50S subunit.  The "S" stands for svedbergs, a unit used to measure how fast molecules move in a centrifuge Fig : structure of 70S ribosome Fig : nucleoid organisation in bacteria Plasmid

 Extra nuclear genetic elements consisting of DNA.  Transmitted to daughter cells during binary fission.  May be transferred from one bacterium to another.  Not essential for life of the cell.  Confer certain properties e.g. drug resistance, toxicity. Flagella  Long (3to12µ),filamentous surface appendages.  Organs of locomotion.  Chemically, composed of proteins called flagellins.  The number and distribution of flagella on th bacterial surface are characteristic for a given species- hence are useful in identifying and classifying bacteria.  Flagella may serve as antigenic determinants(e.g.the H antigens of Gram-negative enteric bacteria).  Presence shown by motility Fig : structure of flagella e.g.hanging drop preparation.

Pilli and fimbriae

Proteins filaments. Shorter and thinner: fimbriae Longer and fewer: pili  Sex Pili : The filaments that are best known for their function in conjugation. Inclusion bodies

Are reserve deposits of bacterial. Cells accumulate nutrient when they are plenty and use when deficient. Major Inclusion bodies are: • Gas vacuoles-allows for buoyancy . • Sulfur granules. • Polyphosphate granules. • Glycogen granules. • Lipid inclusion. • Magnetosomes.